Unexamined patent application DE 34 36 190 A1 describes a method for the electronic control of an automatic vehicle transmission, wherein electrohydraulically actuatable friction elements bring about the shifting between the various transmission ratio steps. A variable characterizing the gear shift, for example the slip time, the shift time, or the speed gradient during the slip time, is compared with a reference variable, wherein a correction value is stored if a predefined deviation is exceeded. This correction value acts in a correcting manner for subsequent gear shifts. In this way, manufacturing related deviations or aging effects are to be compensated for.
Patent U.S. Pat. No. 5,434,779 A describes a pressure control for an automatic transmission, wherein a characteristic map including correction values is used in order to correct the characteristic map values of the normal pressure control. In this case, the correction characteristic map relates to the gear shift type and the accelerator pedal position of the motor vehicle equipped with the automatic transmission. As a result, the ease of gear changes can be improved for various load conditions of the motor vehicle.
During a hydraulic actuation of a shift element, the force acting on the shift element depends on the pressure in the pressure chamber, which acts on the corresponding actuating piston. If this pressure chamber is being rotated, the pressure prevailing therein depends not only on values predefined by the control, but also on the rotational speed of the pressure chamber. If the rotational speed of the pressure chamber increases, the pressure in the pressure chamber increases due to the centrifugal forces acting on the hydraulic fluid. This rotational pressure can be compensated for by providing a pressure compensating cavity. Such a pressure compensating cavity is filled with hydraulic fluid and rotates at the same rotational speed as the pressure chamber. Due to a suitable design of the effective diameter of the pressure compensating cavity, the influence of the centrifugal forces on the pressure in the pressure chamber is compensated for, in that the pressure change of the hydraulic fluid in the pressure compensating cavity counteracts the pressure change in the pressure chamber. As a result, the rotational speed dependence of the force acting on the shift element can be clearly reduced. Such a design is known from patent application DE 10 2013 219 326 A1, by way of example.
Such a pressure compensating cavity is usually filled by the hydraulic system of the transmission. If the pressure supply of the hydraulic system is stopped, the pressure compensating cavity can drain. If the pressure supply of the hydraulic system is activated again, the pressure compensating cavity is filled again. In transmissions for hybrid vehicles or for motor vehicles having a start/stop function of the internal combustion engine, such a changeover between an inactive and an active pressure supply can take place over a very short time. Proceeding from the inactive state, if a pressure chamber for actuating a shift element is to be filled for a short time, a faulty pressure control may occur if the pressure compensating cavity is not yet filled or is filled with only a small amount of hydraulic fluid. This influences the quality of the gear shift in a negative way.